In accordance with the recent development of wireless communication demand for computer communication or the like, a technique which transmits a digital signal or an analog signal in a wide band with high quality is demanded. Due to the width of an occupied band and the shortage of frequencies in the current micromillimeter wave band, various wireless communication systems (for example, video multiplexing transmission system, a wireless LAN, a wireless home link, and the like) using high-frequency bands consisting of an SHF band or higher, i.e., 60-GHz to 70-GHz band, in other words, millimeter waves are researched and developed.
Document 1: Hamaguchi, et al, “Development of Millimeter-Wave Video Transmission System II”, TSMMW '01, P-17, March 2001
Document 2: Hamaguchi et al., “Millimeter-Wave Ad Hoc Wireless Access System”, TSMMW '02, P-1, March 2002
According to Document 1 or Document 2, a “millimeter wave self-heterodyne transmission scheme” which realizes stable communication at low cost in a millimeter wave band is proposed. The effectiveness of the system is principally proved by an application targeted to immobile communication or nomadic communication.
However, the mobile communication system in a millimeter wave band includes problems to be further studied.
For example, one base station can cover only a small area (few-millimeter order) to use a millimeter wave band in mobile communication, so that an arrangement of a base station in relation to mobile stations must be considered as a problem.
Furthermore, since a millimeter wave band has considerably high frequencies, a millimeter-wave-band oscillator having a stable oscillation frequency is still expensive. When a low cost and compact millimeter-wave-band oscillator is applied to a frequency converter or the like, a frequency offset or phase noise occurs as a problem.
In addition, since a millimeter wave band has short wavelengths, communication is easily affected by Doppler shift caused by movement of a mobile station. A method of excluding the influence of the Doppler shift is a problem to be solved.
It is an object of the present invention to provide a wireless communication system which realizes a network configuration and an access point configuration which can appropriately transmit a transmission signal to a receiving station.
It is another object of the present invention to provide a wireless communication system in which a mobile station can stably receive a transmission signal regardless of the accuracy of a local oscillator or Doppler shift.